In a missile system, aerodynamic loads are introduced during flight at the missile fins as a function, for example, of air density or fin angle. The missile fin control system must respond to these loads to maintain flight control. In testing response of such systems, the dynamic response of a loading device must be significantly better than that of the test article that it loads so as to not unrealistically affect performance of the article. Since missile fin control systems are inherently high performance servos, the performance requirements of the load simulator are demanding. It has been the prior art custom to load such systems with passive devices such as mechanical springs or torsion bars or by means of a pneumatic actuator with a large pressure chamber which is the equivalent of a pneumatic spring. There are disadvantages of these devices. For example, they are not adaptable to rapdily switching from an opposing to an aiding or overdrive load which reflect a realistic condition for many applications. They are also inflexible with respect to permitting rapid dynamic variations in loading.